Pendulum support



Dec. 12, 1944. R. a. WRIGHT 2,364,681

PENDJLUM sUPPRT Filed Aug; 25, 1941 77771 ll/ @I Il [OSC/MARIE i I N V E N T E IQ v L Russe/.1. B. Wma/1T ATTDQNEY Patented Dec. 12, 1944 PENDULUM SUPPORT Russell B. Wright, Washington, D. C.

Application August 25, 1941, Serial No. 408,235

(Granted under the act of March 3, 1883, as amended April 5H), 1928; 370 O. G. 757) 4 claims.

The invention describedA herein #may be manufactured and used by or for the Government of the United States for governmental purposes without the payment to me of any royalty thereon in accordance with the provisions of the act of April 30. 1928 (Ch. 460, 45 St. L. 467).

This invention relates to methods and means for supporting and electrically actuating pendulums and particularly to methods and means employing piezo-electric crystals for supporting gravity pendulums. y f

One object of this invention is to decrease as far as possible the pivotal damping of pendulums. Another object of this invention is to provide methods and means for generating electrical impulses of constant frequency under control of a swinging pendulum.

A further object of this invention is to provide a pendulum capable of being set into oscillation at its natural frequency piezo-electrically.

Other and further objects of this invention will be apparent from the detailed description hereinafter when taken in conjunction with the drawingl forming a part hereof and in which Figure 1 is a front elevational view partly in section of a. preferred embodiment of the invention, showing a pendulum partly Ioreshortened together with a flexible pivot member and one `iorm of piezo-electric crystal supporting means and electrodes therefor;

Figure 21s a sideelevational view made at right angles to the showing of Figure 1; and

Figure 3 is a circuit diagram showing schematically the piezo-electric crystals depicted in Figure l with their associated electrodes connected to a vacuum tube oscillator to cause the oscillator to deliver an output frequency controlled in step with the swinging oi the pendulum associated I with those crystals.

where a thin flexible metal member is used, such as shown in the Thompson Patent No. 99,261, granted January l25, 1870.

` To lessen or overcome this undesirable feature,

. the present invention employs a pivotal support for a pendulum comprising a thin flexible ribbon element of quartz which bends to allow the pendulum to swing. This ribbon is made as thin as possible consistent with the weight it is called upon to carry and it is elongated to provide a bendable portion of sufficient length to provide maximum displacement of the pendulum without exceeding the maximum allowable stress therein. In the preferred embodiment this ribbon is made of crystalline or fused quartz, although any material having small elastic hysteresis may be substituted for the quartz. y hysteresis the pendulum will have a low damping action. With this construction the precision obtainable is markedly increased over a knife-edge supported pendulum where erratic, variable frictional forces are inevitable. The precision' is also increased over spring-leaf supported pendulums of 'known types employing' metal spring supports having high elastic hysteresis. These diiilculties may be overcome b y making the thin supporting member of quartz or some other material having small elastic hysteresis.

In addition to the above noted advantages, the present invention provides a pendulum driving or pendulum driven arrangement in which the interconnection between the pendulum proper and the associated apparatus is electrical through the intervention oi' piezo-electric crystals, whereby the pendulum may be utilized to control'the frequency of oscillation of a vacuum tube oscillator of the crystal controlled type. Certain crystals, such as quartz, possess the property o'f developing an electric charge when they are put under pressure or/otherwise stressed, and vice versa; that is, they change in dimensions and Xshape under the action of the electrostatic ileld.

Consequently the frequency of oscillation of a vacuum tu'be oscillator may be controlled by the mechanical stressing of a quartz crystal. Crystal oscillators are well known in the `iield of radio where frequencies o1' thousands oi cycles per second are generated. In the oscillators of the prior art as exemplified in the United States patents of G. W. Pierce, the frequency of oscillation is determined almost solely by the size, shape and physical characteristics of thecrystalitself. In the present invention the effective length of the pendulum determines the frequency at which the piezo-electric crystal is to be stressed.

In the drawing, members I and 2 are piezo' electric, being made of crystalline quartz, while the thin ilexible member 3 is either crystalline or fused quartz. l The piezo-electric members I and Ilare rigidly supported at their upper ends and spaced apart by spacers, such as 4 and l. At their lower ends the piezo-electric members I and 2 are spaced apart by spacers l and l and With a small elasticy by the thin erlible member t. The upper ends oi the crystal members i and t, together with the spacers l and 5, are' 'firmly clamped between members b and i3 constituting a part ci the pen dulum supporting structure. The lower ende of the crystal members'i and 2 together with the spacers and 'i and the upper end oi' the thin nexible member 3 are firmly clamped between the clamping members 'it and il; The lower end oi the thin flexible member il is firmly clamped betweenl the members i2 and i3, which member@ form a support ior the parts depending theres iront.

Electrodes il@ and i5 are disposed on oppeisite sides ci? the cri/stai member 2 and electrodes to and it' are disposed on opposite sides oitlie crystai member G. These electrodes indy b formed ci metai 'oii pasted directly on the re spective sides of the crystal members er they r :y ce sputter-ed or evaporated or otherwise depcsi thereon, but for the utmost in precision should be mounted 'lar enengh from the pienou electric elements to preventy physical contact therewith at ali times, yet close enough to aiect or be affected by the respective crystal menbere.

Bolts i8 pass through the pair oi clamp members i?? and i3 and secure a second pair clamping members l@ and. i2@ thereto. il clamping members i@ and tightly engage thin rlexible member 2i at its upper end, LShe thin iexible member 2l is mounted tc permit ready exure thereoi at right angles to the direc tion of ilexure of the thin flexible member the lower end oi' the flexible member 2i there is attached a pendant comprising twc halves 2li and 23 which are bolted or otherwise clamped toel gether and to 'the member 0i.

The electrodes associated with the pieno-elec= tric members i and a are connected, as shown in Figure 3, to a vacuum tube oscillator 2d when it is desired to generate electrical impulses conf: trolled by the swing or the pendulum ccniprisinr,

pendant i2, 23, iiexible members 2i and 3 and` the piezo-electric elements i and 2.

In the above described apparatus the piezau electric elements l and 2 are cut from the mother crystal with orientation such as to give longitudinal stress when an electrostatic neld is applied in the direction of the thickness dimension. For high precision the orientation should be such as to give the lowest temperature coefficient. With the two elements I and 2 oriented similarly, the electrodes I4, l5, I8 and i1 should be connected as shown in Figures 1 and 3, with electrodes I5 rand I6 connected together and with electrodes Il and i1 connected together, in which case an applied electricalpotential will cause one element to expand while the other element contracts. With an alternating potential of a frequency corresponding to the natural (driven) frequency of the pendulum, it may be sustained in motion if desired. Conversely, if, the pendulum is caused to swing an alternating potential will be produced across the terminals Il and I5, thus facilitating frequency comparison for measurement.

In the above described embodiments all of the elements constituting the pendulum proper and I its supports, lwith the exception of the piezoaesinet electric elements and the bolts, nuts and wasr--A used in clamping the parts together, shouid, -oz precision, be made of i'used quartz or some other material having a low coeillcient of expansion ane. small elastic hysteresis.

In operation the pendulum, comprising pendant 122, 23 and members 2l and i and piezo-electric elements i and swings as shown by the arrows in Figure i, pivoting in part about the fixed aupport G-Q by virtue oi the elasticity er? piezo electric elements i and 2 about the members Gwl by denure of the member ii. The lower flexible member 2i permits bending thereof to compensate ier slight inaccuracies in leveling the supporting members t and The pendulum can be made to swing by the application ci electrical potentials the proper ireoiuency across the pieaoelectric element, or electrical potentials can he generated by swingingv the pendulum, or the swing of the pendulum may be niade to be seiisustaining to sont; he gen-4 eration of electricai osciilations of frequencies hitherto found to be Sfar belowI the of piezaelectric oscillators.

@ther modifications appl ations will he arent those skilled in the art r ail auch are considered to fall with i' the secr nd spirit/ oi' the invention as defined in the appended claims.

is claimed is:

l. .il preeision pendulum comprising can of piezo-electric elements mounted in parada. rela tien and similarly oriented, means for rigidly holding said piezo-electric elements one end, means clamping the opposite ends ci said elements to one end of a thin flexible element suspending a pendulus mass at its opposite end, and means or electrostatically exciting said piezoelectric elements to simultaneouslyl cause lengthening oi one element and shortening of the other element, whereby said pendulus mass swings at itsnatural frequency responsive to the excitation. of said piezo-electric elements at said frequency, pivoting partly in said pair er piezo-electric elements and partly in said thin nexible element.

2. A device in accordance with claim l, in which said thin flexible element is composed of fused quartz.

3. A device for generating electrical impulses at the free swinging periodicity of a pendulum,

comprising a pair of spaced piezo-electric elements mounted in parallel relation andy rigidly held airone end, a member suspending a pendulous mass clamped to the opposite end of said piezo-electric elements, pairs of electrodes embracing said piezo-electric elements for collecting the charges generated thereacross responsive to the swingingcf said pendulum and the consequent stressing of fsaid piezo-electric elements and conductors connecting respective ones of said pairs of electrodes together whereby arithmetical addition of the charges generated across both of said piezo-electric elements is effected.

4. A device in accordance with claim 3, in which the member supporting said penduious mass is a thin ilexible member composed of fused quartz.

RUSSELL B. WRIGHT. 

